Suppose the area of a circle is ${36\pi}$. What is its diameter?
${K = 36\pi}$ ${d = 12}$ First, find the radius: $K = \pi r^2$ , so $r = \sqrt{K / \pi} = \sqrt{{36\pi} / \pi} = {6}$ Now find the diameter: $d = 2r = 2\cdot {6} = {12}$.